compressor surge generally isn't good though

 

Sorry to rain on your parade guys but a lot of you are misguided to what the sound is and the importance of blow off valves and waste gates.

The chattering sound that you hear from high powered cars are their waste gates, the waste gate determines the amount of boost that the turbo is going to produce by vacuum pressure. The waste gate is like a blow of valve but when the turbo produces the desired amount of boost the waste gate will open and allow excess exhaust gas to pass by the exhaust turbine which therefore controls the amount of boost. the chatter sound happens when you let off the gas and the waste gate is venting exhaust gas at a high pressure and it is closing and opening then closing and opening and so on. the waste gate will stay closed at idle and while building pressure because the boost pressure is not at the required level. Along with blow off valve the waste gate can be vented into the atmosphere instead of back into the down pipe which will thus produce a very loud chatter and turbo spool noise.

As for the blow off valve the only purpose of this is to relieve the boost pressure in the intake charge pipe so that it does not have to travel back into the turbo putting huge amounts of stress on the turbine along with slowing the turbine down. If there was no blow off valve then the turbo lag between shifts would be hugely dramatic compared to normal and also your life of the turbo will decrease by a lot around 1/2 or 1/4 regular life of the turbo. The car will not blow if there is no blow off valve because the increased pressure in the charge pipe is caused by the throttle bodies closing thus the are will not go into the engine and must go elsewhere and the only way to go is back through the turbo or through a BOV if you have one.

Hope this clears some stuff up

 

CAN_GTR

that is good information, but i was referring to BOV chatter which usually results from the spring in the BOV being too hard for the boost application

some bov's come with several spring choices for different boost levels,

indeed a wastegate makes noise and is solenoid controlled so i imagine with certain exhaust setups you might hear this

people might install a screamer pipe and this is basically a VTA wastegate pipe, when max boost pressure is achieved and the wastegate starts opening and closing to prevent overboost a ragingly loud noise is heard from the car

it sounds like a shriek or scream, hence it's name

it also sounds kinda jet-plane like because you're hearing air coming off a turbo spinning at probably 180,000+ rpm

 

Hey man, I am sure that the chatter does not come from a blow off valve. The sound is from a waste gate even if they are vented to the down pipe as my brother had a build Supra 7MGTE and he had bypass not a BOV and we could still hear waste gate chatter when he would let off the gas after full throttle.

BOV are also controlled by vacuum pressure like waste gates so that you can set the max pressure for your charge pipe. If they were not controlled by vacuum pressure then having a hard spring in the BOV would lead to the charge pipe over boosting while the throttle body is closed causing damage to the turbocharger and decreased lag. So when the BOV reaches the max psi set by spring rate and vacuum pressure it opens and stays open until the pressure decreases back to standard boost pressure.

Just to add a bit a BOV and waste gate are basically the same thing in a sense, they are both controlled by spring rates and vacuum pressure and they both bypass air from a higher psi area to a lower one.

One thing that I am not sure on is if stock or low powered bypass valves and waste gates use spring rates as well, haven't really looked into this.

 

clarification needed from someone,

i think that we're talking about 2 different things

wastegate and bov have different functions and are on different sides of the turbo

 

yeah sorry I kind of made it sound like I was saying they are the same thing, what i meant was that they are almost identical in the way that they function and they way that they are built (accept for internal waste gates, same thing just different method of achieving the same result). Just to clear it up one is on the charge pipe and relieves excess boost pressure when the throttle body is closed and one control the amount of boost that your turbo will produce.

In essence we are both right about what we are talking about but I think you are trying to say that the chatter is from a BOV and not the waste gate and I am saying the chatter is from a waste gate and not a BOV.

I love constructive arguments, keeps forums interesting!!

peace

 

yeah i do too, i appreciate your comments and i agree with your analysis

stuff like this makes you think a little which is good

 

call me a ricer but I rather have the bov vent into the atmosphere. mine's currently routed back into the intake, but i may alter this. it may idle better too.

 

are you running stand alone?

 

no, but i need to. I'm hitting the max of my current piggy back (unichip) and I need fcon to do the re route.